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AeroEd LLC Aviation Education Resource

TABLE OF CONTENTS 757 GENERAL FAMILIARIZATION SELF-PACED

ATA 21

AIR-CONDITIONING SYSTEM......................................................................................................................................6 Cooling ...............................................................................................................................................................6 Temperature Control ..........................................................................................................................................6 Distribution.........................................................................................................................................................6 Heating ...............................................................................................................................................................6 Pressurization Control ........................................................................................................................................6 Control and Indication ........................................................................................................................................8

COOLING PACK SYSTEM .......................................................................................................................................... 12 Operation.......................................................................................................................................................... 16 The Air Cooling Pack Operation ....................................................................................................................... 16 The Pack Flow Control ..................................................................................................................................... 18 The Pack Temperature Control......................................................................................................................... 19 The AUTO Mode............................................................................................................................................... 19 The STBY-N mode ........................................................................................................................................... 19 The STBY-W Mode........................................................................................................................................... 20 The STBY-C Mode............................................................................................................................................ 20 The OFF Mode.................................................................................................................................................. 20

AIR-CONDITIONING SYSTEM COMPONENTS ........................................................................................................... 23 Flow Control and Shutoff Valve ........................................................................................................................ 23 Primary Heat Exchanger ................................................................................................................................... 24 Secondary Heat Exchanger ............................................................................................................................... 24 Plenum/Diffuser Assembly .............................................................................................................................. 24 Air Cycle Machine............................................................................................................................................. 26 Re-heater.......................................................................................................................................................... 28 Condenser ........................................................................................................................................................ 28 Water Extractor................................................................................................................................................. 30 Split-Duct Water Separator .............................................................................................................................. 30 Low Limit Control Valve ................................................................................................................................... 32 Temperature Control Valve ............................................................................................................................... 33 Automatic-Pack-Temperature Controller .......................................................................................................... 34 Standby-Pack-Temperature Controller ............................................................................................................. 34 Pack Temperature Sensor ................................................................................................................................ 37 Altitude Switches.............................................................................................................................................. 37 Compressor Outlet Temperature Sensor .......................................................................................................... 37 Compressor Outlet Overheat Switch ................................................................................................................. 38 Pack Outlet Overheat Switch ............................................................................................................................ 38 Cabin Air Supply Check Valve .......................................................................................................................... 38 Flow Control Card............................................................................................................................................. 40

ZONE TEMPERATURE CONTROL SYSTEM................................................................................................................ 41

757 General Familiarization (7-2005) ATA 21 - Page 1 For Self-Paced Training Purposes Only

AeroEd LLC Aviation Education Resource Functional Description .............................................................................................................................................. 44

System Temperature Integration (Pack Demand)............................................................................................. 44 Alternate Temperature Control ......................................................................................................................... 44 APU Output Control .......................................................................................................................................... 44 Zone Temperature Control (Auto Mode)........................................................................................................... 45 Off Mode .......................................................................................................................................................... 46 Trim Air Pressure Regulation ........................................................................................................................... 46

ZONE TEMPERATURE COMPONENTS....................................................................................................................... 48 Zone Temperature Sensors .............................................................................................................................. 48 Duct Temperature Sensors............................................................................................................................... 48 Duct Temperature Sensors for the Zone Inlet .................................................................................................. 48 Duct Temperature Sensors for the Mix Manifold ............................................................................................. 48 Duct Overheat Switches.................................................................................................................................... 48 Check Valves for the Trim Air Supply .............................................................................................................. 49 Check Valves for the Trim Air Supply .............................................................................................................. 50 Zone Temperature Selectors............................................................................................................................. 50 Pressure Regulating Valve for the Trim Air System ......................................................................................... 52 The Modulating Valve for the Trim Air............................................................................................................. 53 Zone Temperature Controller............................................................................................................................ 54

CONDITIONED AIR DISTRIBUTION SYSTEM ............................................................................................................ 55 Mix Manifold .................................................................................................................................................... 56 Ground Conditioned Air Connector ................................................................................................................... 56 Flight Deck Conditioned Air Distribution .......................................................................................................... 59 Floor Registers ................................................................................................................................................. 59 Overhead Register ............................................................................................................................................ 59 Windshield Diffuser .......................................................................................................................................... 59 Gaspers ............................................................................................................................................................ 60 Air Inlets .......................................................................................................................................................... 60 Passenger Cabin Conditioned Air Distribution.................................................................................................. 62 Sidewall Riser Ducts ........................................................................................................................................ 62 Overhead Duct.................................................................................................................................................. 62 Sidewall Outlet Ducts ....................................................................................................................................... 62 Return Air Grills ............................................................................................................................................... 62 Overhead Outlets.............................................................................................................................................. 62 Sidewall Outlets ............................................................................................................................................... 62 Galley and Lavatory Outlets.............................................................................................................................. 62

CABIN AIR RECIRCULATION SYSTEM ...................................................................................................................... 64 Control Panel.................................................................................................................................................... 67 Failure Indication ............................................................................................................................................. 67 Recirculation Air Fan........................................................................................................................................ 68 Recirculation Air Filters.................................................................................................................................... 68 Recirculation Air Check Valve........................................................................................................................... 68

THE LAVATORY AND GALLEY VENTILATION SYSTEM............................................................................................. 71 Ventilation ........................................................................................................................................................ 71



Functional Description...................................................................................................................................... 71 Failure Indication ............................................................................................................................................. 71 Aft Equipment, Lavatory, Galley Ventilation Fan............................................................................................... 72 Lavatory and Galley Ventilation Check Valve..................................................................................................... 72 Galley Ventilation Filter .................................................................................................................................... 72 Fan Current Sensors......................................................................................................................................... 72

HEATING SYSTEM - FORWARD & AFT CARGO COMPARTMENTS & SUPPLEMENTAL............................................ 74 FORWARD CARGO COMPARTMENT HEATING SYSTEM................................................................................... 74 Functional Description...................................................................................................................................... 74 Forward Cargo Heat Exchanger (only on some aircraft) ................................................................................... 76 Forward Cargo Heating Flow Fan...................................................................................................................... 76 Forward Cargo Temperature Thermal Switch................................................................................................... 76 Forward Cargo Fan Current Sensor .................................................................................................................. 76 Forward Cargo Heating Inlet Grill ..................................................................................................................... 76

AFT CARGO COMPARTMENT HEATING SYSTEM ..................................................................................................... 78 Functional Operation ........................................................................................................................................ 78 Aft Cargo Heater............................................................................................................................................... 80 Aft Cargo Heating Flow Fan.............................................................................................................................. 80 Aft Cargo Temperature Control Switch............................................................................................................. 80 Aft Cargo Fan Current Sensor .......................................................................................................................... 80 Aft Cargo Heating Inlet Grill ............................................................................................................................. 80

SUPPLEMENTAL HEATING SYSTEM......................................................................................................................... 82 Foot Electric Surface Heaters ........................................................................................................................... 82 Shoulder Air Supply Heater.............................................................................................................................. 82

PRESSURIZATION SYSTEM ...................................................................................................................................... 85 Functional Description...................................................................................................................................... 86 Automatic Pressure Controller.......................................................................................................................... 88 Outflow Valve ................................................................................................................................................... 89 Cabin Pressure Selector Panel ......................................................................................................................... 90

PRESSURE RELIEF SYSTEM ..................................................................................................................................... 92 Positive Pressure Relief Valve .......................................................................................................................... 92 Vacuum Relief Valve ......................................................................................................................................... 94

PRESSURIZATION INDICATION AND WARNING SYSTEM......................................................................................... 95 Altitude Warning System .................................................................................................................................. 95 Altitude Switch ................................................................................................................................................. 95 Differential Pressure Sensor ............................................................................................................................ 96 Pressurization and Indication Warning Module ................................................................................................ 97

EQUIPMENT COOLING SYSTEM ............................................................................................................................... 99 Functional Description Equipment Cooling System Normal Operation........................................................ 100 Fan Check Valve ............................................................................................................................................. 102 Overboard Exhaust Valve ................................................................................................................................ 103 Equipment Cooling Air Fan............................................................................................................................. 104 Equipment Cooling Air Cleaner....................................................................................................................... 105 Fan Fail Sensor (Current Sensor)................................................................................................................... 105



Fan Fail Sensor (Current Sensor)................................................................................................................... 106 Equipment Cooling Low Flow Sensor ............................................................................................................. 107 Equipment Cooling Smoke Sensor.................................................................................................................. 108 Equipment Cooling Control Card..................................................................................................................... 109



AIR-CONDITIONING SYSTEM

The air-conditioning system maintains airplane environmental control for the comfort of passengers and crew. The total system is made up of the conditioned air distribution system, pressurization control system, cargo compartment heating system, cooling system and temperature control system.

Cooling Cooled air is supplied to the distribution system by two air cooling packs. The pneumatic system provides source air to the packs. The ram air system assures pack temperature control. The pack indicating system allows flight deck monitoring of pack operation. The equipment cooling system removes heat generated by electrical and electronic equipment in the flight compartment, forward equipment area, main equipment racks, and aft equipment area.

Temperature Control The temperature control system regulates the environment within the airplane's three primary zones. Cooled air mixes with hot "trim" air to obtain the desired temperature at each zone. Monitoring of the system is provided by valve position indication and the zone temperature indication system.

Distribution The distribution system channels temperature-controlled air to the flight deck and passenger cabin through a network of distribution ducts. The main mix manifold combines cooled air from the air cooling packs with recirculation air drawn from the passenger cabin. The air is channeled to the flight deck through ducts and to the passenger compartment through risers, overhead ducting and outlets. Separate exhaust ducting provides positive ventilation for all lavatory and galley areas.

Heating Independent cargo compartment heating systems provide temperature control for the forward, aft and bulk cargo compartments. The supplemental heating system channels heated air to the captain's and first officer's foot and shoulder areas.

Pressurization Control The air conditioning system provides pressurization control by regulating the amount of air discharged from the airplane. Backup positive and negative pressurization relief systems prevent the cabin pressure from exceeding established limits. Pressurization indication and warning systems allow the operator to monitor the pressurization control system.



Control and Indication Control selectors and switch lights on the pilot's overhead panel P5, and one control selector on the right side panel P61, allow control of all air-conditioning systems. Warning lights, position indicators and other gages on the P5 panel provide partial indication of system operation. The Engine Indication and Crew Alerting System provide the remaining indication for the air conditioning system. EICAS provisions include two cathode-ray tube (CRT) display screens on the pilot's center instrument panel P2, a display select panel on the forward electrical control stand P9, and an EICAS maintenance panel on the right side panel P61. EICAS displays primary engine parameters on the upper CRT. Warning, caution, and advisory messages also appear on the upper CRT during certain system malfunctions. Aural tones occur in the flight deck with each of the above types of messages. Two other types of messages may also appear; status or maintenance. These two types of messages both appear on the lower CRT only when called upon by an operator. Status messages display data on the current status of operation and may be called upon by selecting the STATUS switch on the display select panel. The airplane may be either in-flight or on the ground. Maintenance messages are available only on the ground by selecting the ECS/MSG switch on the EICAS MAINT panel. Current maintenance information is usually displayed unless a recorded page is called up. A recorded page is a page with information about the status of the system in-flight when certain failures occurred. These are called AUTO EVENTS and are called up by selecting the AUTO EVENT READ switch on the EICAS MAINT panel.



EICAS ECS MAINTENANCE PAGE



COOLING PACK SYSTEM

The cooling pack system is used to decrease the temperature of a supply of air. The output of the cooling pack system is cold air. This cold air is supplied to all of the necessary airplane compartments by the conditioned-air-distribution systems. Other systems are necessary for the cooling pack system to operate. The cooling pack system uses a supply of air from the pneumatic system. This is hot air from the engines, the APU, or a ground air source. The cooling pack system also uses a supply of air from the ram air system. This is cold air which does not enter the air cooling packs. It is used to decrease the temperature of the air in two of the heat exchangers in each air cooling pack. The temperature control system sends a signal for the necessary output of the cooling pack system. The cooling pack system is made of these components:

1. Two air cooling packs; each has these components:

a) A primary heat exchanger b) A secondary heat exchanger c) An air cycle machine (which has a turbine, a compressor, and a fan) d) A split-duct water separator e) A re-heater f) A condenser g) A water extractor h) A low-limit control valve i) A temperature control valve j) A compressor-outlet overheat switch k) Two compressor-outlet temperature sensors l) Two pack temperature sensors m) A plenum/diffuser assembly

2. Two automatic pack-temperature controllers 3. One standby pack-temperature controller 4. Two flow control cards 5. Two flow-control-and-shutoff valves 6. Two pack-outlet overheat switches 7. Two cabin-air-supply check valves 8. Two altitude switches.

Most of the components in the cooling pack system are interchangeable between the left and right systems. The only component that is not interchangeable is the standby pack temperature controller, because there is only one of them on the airplane.


AeroEd LLC Aviation Education Resource NOTES:



Operation The cooling pack system puts out a specified amount of air at a specified temperature. The Functional Description of the cooling pack system is divided into three parts:

1. The Air Cooling Pack Operation tells what happens to the air as it flows through the air cooling pack. 2. The Pack Flow Control tells how the cooling pack system gets the necessary amount of air from the air

cooling pack. 3. The Pack Temperature Control tells how the cooling pack system gets the necessary air temperature from

the air cooling pack.

The Air Cooling Pack Operation The air cooling pack is pneumatically operated. It operates only when a supply of air goes into it. The flow-control-and- shutoff valve lets air enter the air cooling pack. Thus, when the flow-control-and-shutoff valve is open, the air cooling pack is ON. When the flow-control-and-shutoff valve is closed, the air cooling pack is OFF. Air from the flow-control-and-shutoff valve first flows into the primary heat exchanger. The primary heat exchanger causes the air temperature to decrease. Then the pressure and the temperature of the air are increased as it flows through the air-cycle-machine compressor. The secondary heat exchanger again causes the air temperature to decrease. Then the water is removed from the air. The split-duct water-separator removes an initial amount of water as the air moves from the secondary heat exchanger. Then the air flows through the re-heater and the condenser, which both cause the air temperature to decrease. The low temperature of the air causes water drops. Subsequently, as the air flows through the water extractor, the water extractor removes the water. The water extractor puts the water in the ram air system or lets it flow overboard. After the water is removed from the air, the air flows in the other direction through the re-heater. This causes the temperature to increase before it goes into the air-cycle- machine turbine. The air-cycle-machine turbine decreases the pressure and the temperature of the air. The energy from the expanded air makes the air cycle machine operate. Subsequently, the air again flows through the condenser. This causes the air temperature to increase as it goes from the air cooling pack. The low-limit-control valve and the temperature control valve lets some of the air go around the air cycle machine. This hot air flows to the turbine outlet to prevent ice. Also, because a smaller amount of air flows through the air cycle machine, the speed of the air cycle machine decreases. This causes the compressor outlet temperature to decrease and the air- cooling-pack-outlet temperature to increase.


AeroEd LLC Aviation Education Resource Air Cooling Pack Operation (Continued): Small amounts of air flow through the tubes in the air cooling pack. This air has special uses. Some tubes supply air to the low-limit-control valve to cause it to open or close. Some air goes from the secondary heat exchanger through a tube to get water from the water extractor. Also, some air goes from the compressor flows to the condenser and the turbine outlet to prevent ice.

The Pack Flow Control The amount of air that flows through the air cooling pack is controlled by the flow control cards. Each flow control card controls one flow-control-and-shutoff valve. The flow-control- and-shutoff valves permit a controlled amount of air into each air cooling pack. The flow-control-and-shutoff valves open when the L or R PACK selector, on the pilot's overhead panel P5, is not in the OFF position. The selector sends a signal to the flow control card to open the flow-control-and-shutoff valve. The flow control card causes the flow-control-and-shutoff valves to go into the normal flow mode or the high flow mode. A compressor overheat condition occurs when the compressor discharge temperature is more than 490F (254C). At 490F (254C), the compressor outlet overheat switch closes and sends an overheat signal to the flow control card. Also at 490F (254C), the compressor outlet sensor sends an overheat signal through the pack temperature controller to the flow control card. The flow control card then latches in the overheat position and causes the following conditions to occur:

1. The flow-control-and-shutoff valve closes. 2. The PACK OFF and INOP lights, on the P5 panel, come on. 3. The advisory messages L (R) PACK OFF and L (R) PACK TEMP show on the EICAS display. 4. The AUTO/MANUAL relays are not energized (this prevents control of the air cooling pack by the

automatic-pack- temperature controller). 5. The backup-temperature-control card causes the air cooling pack to go to the cool mode (the ram air

doors and the temperature control valve open).

A pack overheat condition occurs when the pack discharge temperature is more than 190F (88C). At 190F (88C), the pack overheat switch closes and sends an overheat signal to the flow control card. The flow control card then latches in the overheat position and causes the following conditions to occur:

1. The backup temperature control card causes the pack to go the full cold mode (the ram air doors fully open and the temperature control valve closes).

2. The AUTO/MANUAL relays are not energized (this prevents control of the air cooling pack by the automatic-pack- temperature controller).

3. The INOP light, on the P5 panel, comes on. 4. The advisory messages L (R) PACK TEMP show on the EICAS display.

The air cooling packs operate as usual when the temperature returns to the normal range and the RESET switch, on the P5 panel, is pushed.



The Pack Temperature Control The air-cooling-pack-outlet temperature is controlled by the automatic-pack-temperature controllers, the standby-pack- temperature controller, or the backup-temperature-control cards. Each component controls the air cooling packs for a different temperature mode. The temperature mode is controlled by the position of the L and R PACK selectors, on the P5 panel (the L and R PACK selectors can be in different temperature modes at the same time). The temperature modes are AUTO, STBY-N, STBY-W, STBY-C, and OFF.

The AUTO Mode

1. In the AUTO mode, the automatic-pack-temperature- controllers control the air cooling packs. AC power is always supplied to each controller. When the L or R PACK selector is in AUTO, the controller sends signals through the AUTO/MANUAL relays to control the position of the ram air doors and the temperature control valve. Also, because the low-limit-control valve relay is not energized, the controller can send signals to the low-limit-control valve.

2. The necessary air-cooling-pack-outlet temperature is sent as a signal to the automatic pack temperature

controller by the zone temperature controller. This is the pack demand signal. The automatic-pack-temperature controller compares the pack demand signal to the pack- temperature-sensor signal. The difference between the signals causes an error. The error controls the signal that is sent to the ram air door actuators and the temperature control valve.

3. When the airplane is on the ground, the ram air doors stay fully open. The temperature control valve

position changes to control the air-cooling-pack-outlet temperature.

4. The compressor outlet temperature sensor supplies input to the controller to prevent an overheat condition.

5. The altitude switch supplies input to the controller to change the lower water separator temperature limit

from 35F (1.7C) to 0F (-18C). The controller closes at 31,000 feet. This sends a signal to the controller to change the limit.



The STBY-N mode 1. In the STBY-N mode, the backup-temperature-control card and the standby-pack-temperature-controller

controls the air cooling packs. When the L or R PACK selector is in STBY-N, the AUTO/MANUAL relays are not energized. This lets AC power flow to the controller. It also supplies 28-volts DC to energize the low-limit-control- valve-control relay (ground is supplied in the backup- temperature-control card). The controller sends an open or a close signal through the control relay to the low-limit-control valve. The backup-temperature-control card causes the ram air doors to be fully open and the temperature control valve to be fully closed. Also, no current is supplied to the torque motor of the flow-control-and-shutoff valve.

2. The demand signals for the standby-pack-temperature controller are programmed to be 40F (4.5C) (for the pack temperature) and 450F (232C) (for the compressor outlet temperature). The controller compares the temperature sensor signals to the set demand signals. The difference of the signals causes two error signals. The greatest error signal controls the position of the low limit control valve.

The STBY-W Mode 1. In the STBY-W mode, the backup-temperature-control card controls the air cooling packs. 28-volts DC is

always supplied to the backup-temperature-control card. When the L or R PACK selector is in STBY-W, the AUTO/MANUAL relays are not energized. This lets the card send signals through the AUTO/MANUAL relays to the ram air doors and the temperature control valve.

2. In the STBY-W mode, the backup-temperature-control card causes the ram air doors and the temperature

control valve to be fully open. The low-limit-control valve stays closed unless it is pneumatically opened.

The STBY-C Mode 1. In the STBY-C mode, the backup-temperature-control card controls the air cooling packs. 28-volts DC is

always supplied to the backup-temperature-control card. When the L or R PACK selector is in STBY-C, the AUTO/MANUAL relays are not energized. This lets the card send signals through the AUTO/MANUAL relays to the ram air doors and the temperature control valve.

2. In the STBY-C mode, the backup-temperature-control card causes the ram air doors to be fully open and

the temperature control valve to be fully closed. The low- limit-control valve stays closed unless it is pneumatically opened.

The OFF Mode 1. When the L or R PACK selector is OFF, the ram air inlet doors and the temperature control valve is

controlled by the air/ground relays. When the airplane is on the ground, the ram air doors will be fully open and the temperature control valve will be fully closed. When the airplane is in the air, the ram air doors will be fully closed and the temperature control valve will be fully open. The low-limit-control valve will stay closed unless it is pneumatically opened.

2. Whenever the left or right flow control valve is closed, the applicable (L or R) PACK OFF light, on the P5

panel, will come on and the EICAS message L or R PACK OFF will be shown on the upper display.



AIR-CONDITIONING SYSTEM COMPONENTS

Flow Control and Shutoff Valve The flow-control-and-shutoff valve lets a controlled amount of air flow from the pneumatic system into the air cooling pack. There are two valves, one for each air cooling pack. Each valve is installed forward and outboard of its air cooling pack. The flow-control-and-shutoff valve lets air into the air cooling pack at two different flow rates. Each cooling pack can supply about 80 percent of the air that is usually supplied by two cooling packs. The mechanical-manual-override valve supplies a way for the flow control valve to be manually closed.



Primary Heat Exchanger The primary heat exchanger is a plate-fin, single-pass, cross-flow, air-to-air heat exchanger. Hot air from the flow-control-and-shutoff valve enters the top of the primary heat exchanger. It flows first to the aft end of the heat exchanger. Then it flows forward, through some of S-turns, to the heat exchanger outlet. Cold air flows at a right angle to the hot air. The air temperatures change as the heat transmits through the thin plate fins. An access door on each side of the heat exchanger supplies an access to clean it.

Secondary Heat Exchanger The secondary heat exchanger is almost the same as the primary heat exchanger. One difference is that the secondary heat exchanger is wider. Also, it has a heavy fin on the cold air inlet side, to prevent damage from hail. Hot air for the secondary heat exchanger comes from the compressor outlet on the air cycle machine.

Plenum/Diffuser Assembly The plenum/diffuser assembly has two main parts; the plenum and the diffuser. The fan in the air cycle machine and a space around the fan are in the diffuser. The plenum, which is the outer part, is made of fiberglass. An access door in the plenum supplies access to clean the primary heat exchanger. The plenum/diffuser assembly connects the air cycle machine, the primary heat exchanger, and the ram air outlet duct. It lets air flow from the primary heat exchanger outlet to the ram air outlet door. The plenum makes the air from the primary-heat-exchanger outlet flow to the diffuser inlet. The air-cycle-machine fan blows air through the diffuser to the ram air exhaust duct. The space around the fan, when necessary, lets more air flow through the diffuser. The plenum and the space are made so that air cannot re-circulate back into the plenum.



Air Cycle Machine The air cycle machine is divided into three parts; a fan, a compressor, and a turbine. Each part has a different impeller. All three impellers are attached to the same shaft. The shaft is held in its position by three air bearings. Lubrication of the air bearings is not necessary. Each part of the air cycle machine has its own air inlet and outlet. The turbine also has an extra inlet and three tubes connected to it. The air-cycle-machine fan is used to draw air through the primary and secondary heat exchangers. When the airplane is in flight, air flows through the heat exchangers because the ram air inlet door is open. When the airplane is not in flight, air will only flow through the heat exchangers when the fan pulls it through. The air-cycle-machine compressor increases the temperature and the pressure of air from the primary heat exchanger. The outlet from the compressor flows through a water-removal process. The water is removed more easily because of the high air pressure. The air-cycle-machine turbine causes the shaft to turn. The turbine decreases the temperature and the pressure of the air. The low temperature at the turbine outlet may cause ice on the turbine outlet. To prevent ice or to decrease the air temperature in the cooling pack, hot air is supplied to the turbine outlet. The supply of hot air is controlled by the low-limit-control valve and the temperature control valve. One of the tubes connected to the turbine also supplies hot air from the compressor outlet. The second tube supplies the turbine outlet pressure to the low limit control valve. The third tube supplies cold air to the water extractor inlet.



Re-heater The re-heater is a plate-fin, single-pass, cross-flow, air-to-air heat exchanger. The plate-fins are at right angles to each other. The re-heater decreases the air that flows from the secondary heat exchanger to the condenser. It also increases the temperature of the air that flows from the water extractor to the turbine. The temperatures are changed in the re-heater as the heat of the air is transmitted through the thin plate-fins.

Condenser The condenser is a plate-fin, single-pass, cross-flow, air-to-air heat exchanger. The core has two heat transfer matrices, which are separated by a space. The cold air side of the core also has tubes of hot air. Each heat transfer matrix is brazed together as a unit. The housing assembly has two inlets and two outlets. It also has two tubes connected to it. The housing assembly is welded to the core. All the parts of the condenser are made of aluminum alloys. The condenser changes the temperature of two supplies of air. The heat of the air supplies is transmitted through the thin plate-fins. The temperature of the air that flows from the re-heater to the water extractor is decreased. This causes the water in the air to condense so it can be easily removed in the water extractor. The temperature of the air that flows from the turbine outlet to the pack outlet is increased. This causes the air to be above the temperature that would make ice. One of the tubes is connected to the hot air inlet of the condenser. The tube supplies hot air from the compressor outlet to the hot air tubes on the cold air side of the condenser. The hot air tubes prevent ice on the cold air inlet of the condenser. The other tube is connected to the cold air outlet of the condenser. This tube supplies air pressure to the low-limit-control valve.



Water Extractor The water extractor has two main parts; the inlet duct and the collector. The inlet duct has a set of helical vanes, brazed to the inner wall of the duct. The helical vanes do not move. The collector has a perforated inner shell, an outer shell, and a sump. The collector isolates the water from the air and collects the water in the sump. Two tubes are connected to the outer shell. A drain tube is connected to the sump. All of the parts of the water extractor are made of aluminum alloys. The air from the condenser has many small droplets of water. As the air flows into the water extractor, the helical vanes cause the air to turn. As the air turns, the centrifugal force pushes the water out to the duct wall (the water is pushed farther out than the air because the water is heavier). In the collector part of the water extractor, the inner shell isolates the air/water near the duct wall. The air can flow through the perforations in the inner shell, but the water cannot. Thus, the water flows through the outer shell and into the sump. The water in the sump then flows to the water spray nozzle of the ram air cooling system. If the sump becomes full, the water flows overboard through one of the ports to the outer shell. The other port connected to the outer shell supplies water to the sump from the split-duct water separator.

Split-Duct Water Separator The split-duct water separator removes water from the air that flows from the secondary heat exchanger to the re-heater. The water that collects in the split-duct water separator is supplied to the sump in the water extractor.



Low Limit Control Valve The low-limit-control valve controls the flow of hot air from the primary heat exchanger inlet to the air-cycle-machine turbine outlet. Air that flows through the low limit valve does not go through the air cycle machine. This air is used to prevent ice in the turbine outlet and to prevent an overheat condition of the air cycle machine. The low-limit-control valve is a 2-inch diameter, pneumatically-controlled, butterfly valve. It has two differential pressure servo assemblies, an electromagnetic control valve, a pneumatic actuator, a reference pressure regulator, a valve flow section, and a valve position indicator.



Temperature Control Valve The temperature control valve is used to control the temperature of the air-cycle-machine-compressor outlet. To do this, it controls the amount of air that flows through the air cycle machine. If more air flows through the temperature control valve, then less air flows through the air cycle machine. The less air that flows through the air cycle machine, the slower it operates. Thus, the temperature at the compressor outlet decreases. The temperature control valve is a 3-inch diameter, electrically controlled and operated, butterfly-type valve. It has a rotary electromechanical actuator, a valve flow section, and a linear variable resistor assembly. When power is supplied to the electric motor, it turns the gears, which turns the output shaft. The output shaft turns the butterfly shaft. The butterfly shaft turns the butterfly plate, the visual position indicator, and the wiper arm of the linear variable resistor assembly. The 1K ohm resistor supplies a position signal to the EICAS computers. The 10K ohm resistor supplies a position signal to the automatic pack temperature controller. The valve can open or close manually. When the manual override knob is turned, the clutch lets the output shaft turn. The clutch holds the butterfly plate in the set position.



Automatic-Pack-Temperature Controller Two interchangeable automatic-pack-temperature controllers are used to control the air cooling packs. One controls the right cooling pack system and the other controls the left cooling pack system. The automatic-pack-temperature controller is a box that has a microprocessor. The microprocessor controls the air-cooling-pack- outlet temperature and monitors the system for failures. The front panel of the controller has lamps to show if a failure occurs. The front panel also has switches and instructions to do the built-in test equipment (BITE). The controllers are in the E6 rack of the aft equipment center, or they can be found on the E3 rack of the main equipment center. Each automatic-pack-temperature controller controls these components for each air cooling pack:

1. The temperature control valve 2. The ram-air-inlet-door and the ram-air-exhaust-door actuators of the ram-air-cooling system 3. The torque motor of the flow-control-and-shutoff valve 4. The low-limit-control valve, when the system is not in the STBY-N mode

Standby-Pack-Temperature Controller The standby-pack-temperature-controller is a box which has two microprocessors. Each microprocessor controls the left or the right air cooling pack. They only operate when the applicable cooling pack system is in the STBY-N mode. The microprocessors also monitor parts of the cooling pack system for failures. The front panel of the standby pack temperature controller has lights that come on when a failure occurs. It also has switches and instructions to do BITE. In the STBY-N mode, the standby-pack-temperature controller controls the low-limit-control valve. The position of the low-limit-control valve controls how fast the air cycle machine turns. The speed of the air cycle machine controls the compressor outlet temperature and the air-cooling-pack-outlet temperature.



Pack Temperature Sensor For each air cooling pack, two pack temperature sensors supply a resistive signal of the temperature at their positions. One pack temperature sensor sends a signal to the standby-pack-temperature controller. The other pack temperature sensor sends a signal to the applicable (left or right) automatic-pack-temperature controller. The pack temperature sensors are installed on the outlet of the water extractor. Each pack temperature sensor has two series-connected glass-sealed thermisters in a stainless steel probe. The automatic-pack-temperature controller compares the pack demand signal (from the zone temperature controller) with the pack temperature sensor signal. The difference between the signals is the pack error. Then it uses the pack error to control the positions of the ram air door actuators and the temperature control valve. The standby-pack-temperature controller compares the pack temperature sensor signal to a value of 40F (4C) to get the pack error. Then it uses the pack error to control the position of the low-limit-control valve.

Altitude Switches Each altitude switch sends a signal to the applicable (left or right) automatic pack temperature controllers. The controllers change the minimum temperature limits of the air cooling packs to make allowance for the altitude. The switches are installed in the forward end of the left ECS bay, to the left of the cabin air supply check valve. The altitude switch is a pressure sensing aneroid, at an altitude of 31,000 feet, the aneroid closes the electrical switch. When the altitude switch closes, the automatic-pack-temperature controller changes the limit of the air cooling pack temperature from 35F (1.7C) to 0F (-18C). At low altitude the 35F (1.7C) temperature limit is used to prevent ice at the condenser and the water extractor.

Compressor Outlet Temperature Sensor For each air cooling pack, two compressor-outlet-temperature sensors supply a resistive signal of the temperature at their position. One sensor sends a signal to the automatic-pack-temperature controller. The other sensor sends a signal to the standby-pack-temperature controller. The sensors are installed adjacent to each other, at the air-cycle-machine-compressor outlet. Each sensor has a platinum element which is hermetically sealed in a stainless probe. The automatic-pack-temperature controller uses the signal to control the position of the temperature control valve. The standby pack temperature controller uses the signal to position the low-limit-control valve. The position of these two valves controls the compressor outlet temperature.



Compressor Outlet Overheat Switch In each air cooling pack, a compressor-outlet-overheat switch is installed at the air-cycle-machine-compressor outlet. The switch is a thermal protective device. When it closes, it sends a signal to the flow control card that an overheat condition has occurred. The switch closes when the temperature is greater than 490F (254C). The switch opens again when the temperature is less than 450F (232C).

Pack Outlet Overheat Switch The pack-outlet-overheat switch is at the condenser outlet. The switch is a thermal protective device. When the pack outlet becomes too hot, the switch sends a signal to the flow control card. The switch closes when the temperature is greater than 190F (88C). The switch opens again when the temperature is less than 160F (71C). The pack-outlet-overheat switch has a temperature-sensitive element with a bimetallic, snap-acting disc. At a specified temperature, the disc moves suddenly to its opposite shape. This causes the switch to close.

Cabin Air Supply Check Valve The cabin-air-supply-check valve prevents the flow of air from the mix manifold into the air cooling packs. The check valve has a spring, a flapper plate, and a stop. The top of the flapper plate is attached by a horizontal hinge to the inside of the check valve. The spring is installed on the hinge to push against the flapper plate. A stop is installed on the top of the check valve to limit how far the flapper can move. When no air is in the system, the spring keeps the flapper plate closed. When the air flows from the air cooling pack to the mix manifold, it pushes the flapper plate open. The air cannot flow in the opposite direction because the flapper plate can only move in the one direction. Thus, the check valve prevents the flow of air from the mix manifold to the air cooling pack.



Flow Control Card The flow control card is in the P50 card file in the main equipment bay. The card controls the position of the flow-control-and-shutoff valve. It also controls the indications that show when an overheat condition occurs.



ZONE TEMPERATURE CONTROL SYSTEM

The primary (zone) temperature control system controls the temperature of the air given to each cabin zone. The system uses a mixture of warm pneumatic air and cool air from the air cooling packs. This will give satisfactory air temperature for the passenger and crew. The primary (zone) temperature control system includes the components that follow:

1. One zone temperature controller 2. Three trim air modulating valves 3. Two check valves for the trim air supply 4. One pressure regulating valve for the trim air supply 5. Three zone temperature sensors 6. Three duct overheat switches 7. Five duct temperature sensors 8. Temperature selector switches for three zones 9. Three amber INOP warning lights.

The temperature of the conditioned air is controlled with the trim air from the downstream side of the flow control and shutoff valve. A mixture of trim air, cooling pack air and recirculation air are used to supply the necessary air temperature. The air temperature can be controlled for each cabin zone; the flight compartment, forward passenger cabin, and aft passenger cabin. The zone temperature controller uses an input temperature from each zone to operate the temperature control system automatically. This input temperature gives the necessary demand to the controller for an increase or decrease in temperature for each zone. The controller uses the demand signal to operate the three modulating valves. The modulating valves control the mixture of warm air and cool air that is supplied to each zone. The primary (zone) temperature indication system supplies a visual indication of the temperature control system. Three modulating valves for the trim air supply are installed in the trim air ducts for each zone, downstream of the pressure regulating valve. The modulating valve positions are electrically adjusted. These valves supply the necessary air temperature to the flight compartment, the forward passenger zone, or the aft passenger zone. The temperature control system contains two check valves for the trim air supply. The check valves are installed in the trim air ducts for each zone. The check valves will not let trim air go into the pack inlet if the air cooling pack stops. The pressure regulating valve for the trim air system controls the pressure of the pneumatic system air that is supplied to the modulating valves. A TRIM AIR switch-light on the pilot's overhead panel, P5, controls the valve position.


AeroEd LLC Aviation Education Resource Zone Temperature Control System (Continued): A duct overheat switch is installed in the duct that goes to each cabin zone. The overheat switch operates as a thermal protective device and closes the applicable modulating valve if the zone duct temperature increases more than 190F. There are five duct air temperature sensors. The sensors get input of the temperature of the supply air that goes into the zone ducts and the two mix manifold outlets. The sensors also supply inputs to the zone controller and pack controllers. There is one temperature sensor for each of the three cabin zones. Each sensor sends a temperature signal to the zone temperature controller. The temperature sensor for the flight compartment also sends a temperature signal to the left pack temperature controller. The temperature sensor for the forward zone also sends a temperature signal to the right pack temperature controller. There is one temperature selector switch for each cabin zone, installed on the pilots' overhead panel, P5. These switches permit the selection of the AUTO control of the temperature control system.



Functional Description

System Temperature Integration (Pack Demand) The zone temperature controller calculates a temperature demand signal for the pack. The demand signal is calculated when the controller compares the inputs of the temperature selector switch for the zone and the zone temperature sensor. The zone temperature controller finds the lowest of the three temperature inputs and sends that signal to the pack temperature controllers as pack demand. The pack demand is the signal from the controller that will change the output of the pack. The pack temperature controllers also receive the temperature inputs from the air temperature sensors in the mix manifold duct. These temperature inputs are then sent to the zone temperature controller. The zone controller finds the lowest of the two mix manifold temperature signals. The lowest signal is used as a reset temperature for the pack demand signal. This lowest temperature corrects the pack demand signal to include the effect of re-circulated air mixed with conditioned air from the air conditioning packs. The pack demand is sent to a new valve until the mix manifold temperature is the same as the zone with the highest temperature. The zone temperature controller then closes the modulating valve for the coolest zone and adjusts the modulating valves for the other two zones. This will supply the necessary zone inlet temperatures.

Alternate Temperature Control The pack demand signal is gone when there is a zone controller failure or all temperature selector switches are out of the AUTO position. When the pack demand signal is gone, the pack controllers are set to a 75F (24C) alternative mode. In the alternative mode the system is set to a two zone control operation. This causes the input from the forward zone to control the right pack and the input from the flight compartment to control the left pack. An alternative signal in the zone temperature sensor supplies applicable pack controllers with the flight compartment or forward zone temperature. Each pack controller uses its alternative sensor. An alternative pack command is supplied to compare the sensor value with the set value of 75F (24C).

APU Output Control The zone controller also supplies a command to the Auxiliary Power Unit (APU) to control the quantity of bleed air to the packs during ground operation. The APU controller uses this command for the supply temperature to give the APU output. The input signal will stay at a minimum until the pack and trim controls give the maximum available heat or cooling. The APU command signal increases with larger demand to give the necessary output.



Zone Temperature Control (Auto Mode) The zone temperature controller operates with 115-volts AC power. Automatic temperature control is supplied when these conditions occur:

1. The temperature selector switches for all three zones are in the AUTO position 2. The selector switch for the pack mode is in the AUTO position 3. The TRIM AIR switch-light is ON

The AUTO input controls the temperature between 65F (18C) and 85F (29C). During correct automatic mode operation, the zone temperature controller adjusts the modulating valve for the applicable zone. The controller adjusts the modulating valve to supply the conditioned air from a correct mixture of the mix manifold air and the trim air supply. This mixture of air will supply the necessary air temperature in each cabin zone. The temperature selector switch for each zone has many different positions to get automatic temperature control. These positions can be the AUTO (12 o'clock position), AUTO W, AUTO C or in between the AUTO W and AUTO C positions. The AUTO position sends a temperature signal equivalent to 75F (24C) to the zone temperature controller to supply a pack or an APU demand signal. The AUTO W position sends a temperature signal to the controller that is equivalent to 85F (29C). The AUTO C position sends a temperature signal to the controller that is equivalent to 65F (18C). In a condition that is too hot (190F, 88C), the applicable flight compartment, forward, or aft zone duct overheat relay energizes. The energized overheat relay does not permit the zone temperature controller to adjust the modulating valves. The relay closes the valves with 28-volts DC. The overheat relay causes the INOP light on the pilot's overhead panel, P5, to come on for the applicable zone. The EICAS will also show the FLT DECK TEMP, FWD CABIN TEMP or AFT CABIN TEMP level C display messages. These EICAS messages are auto events for the environmental control systems (ECS) (Ref 31-41-00). An overheat relay does not permit the zone temperature controller to monitor the applicable zone's temperature control components. An INOP condition can also occur. An INOP condition shows a failure is in a control circuit for the cabin zone. The zone temperature controller will find the failure. An INOP condition also removes the temperature input signal, for the applicable zone, from the pack and APU circuits. The zone temperature controller supplies a ground to permit the INOP light to come on. This will also cause the EICAS messages, FLT DECK TEMP, FWD CABIN TEMP, or AFT CABIN TEMP, to be shown. The duct overheat relay for the forward or aft zone also energizes which will close the applicable modulating valve with 28-volts DC. The zone temperature controller will monitor the LRUs for the applicable zone.



Off Mode The off mode does not permit the trim air into the applicable zone. Through the flight compartment, forward or aft zone overheat relay the modulating valves are closed with 28-volts DC. The zone temperature selector, in the OFF position, will cause the INOP light for that zone to come on. The EICAS messages, FLT DECK TEMP, FWD CABIN TEMP, or AFT CABIN TEMP, will also come on for that zone. These EICAS messages are ECS auto events. In the off mode, the zone temperature controller will not monitor the components for that zone.

Trim Air Pressure Regulation Trim air goes through the flow control and shutoff valves. The trim air will then push open the check valves for the trim air supply. The air then flows to the pressure regulating valve. The pressure regulating valve controls the pressure of the trim air to 4 PSI above the cabin pressure. This keeps the trim air pressure to a limit to decrease the noise of the air that goes through the modulating valves and their duct. The TRIM AIR switch-light on the P5 panel, controls the pressure regulating valve. The regulating valve operates with 28-volts DC power. Push the switch-light to the on position to open the valve. Push the switch-light to the off position to keep 28-volts DC power away from the valve. With the switch-light in the off position the valve closes and the yellow OFF part of the switch-light comes on. The level C message, TRIM AIR, is also shown on the EICAS display.



ZONE TEMPERATURE COMPONENTS

Zone Temperature Sensors The zone temperature sensors are dual element sensors. Each element has two glass sealed thermistors connected in series and are fully sealed in a stainless steel probe-type housing. The temperature sensor measures the air temperature for each cabin zone. The thermistor operates at low current levels to keep to a minimum the temperature changes because of the effect of internal sensor heat. The resistance in each thermistor increases when the input temperature decreases and the resistance decreases when the input temperature increases. The input temperature is sent electrically to the zone temperature controller and to the pack temperature controllers.

Duct Temperature Sensors The duct temperature sensors are one element sensors that have two thermistors that are glass sealed and connected in series. The thermistors are sealed in probe-type housing with an electrical connector that is part of the thermistor and housing. The sensor is installed on a three-hole flange with a gasket. The sensor has a temperature control range of 35F (1.7C) to 180F (82C) and an operating temperature range of -65F (-54C) to 350F (177C).

Duct Temperature Sensors for the Zone Inlet A duct temperature sensor is installed in the inlet duct for each cabin zone. Each sensor supplies a temperature signal to the zone temperature controller.

Duct Temperature Sensors for the Mix Manifold Two duct temperature sensors are installed on the mix manifold. Each sensor supplies a temperature signal to a pack temperature controller.

Duct Overheat Switches The zone duct overheat switch includes a liquid-filled probe, a housing, and an electrical connector. The housing includes a diaphragm welded to the housing, a spring and retainer, and a switch. The spring holds the diaphragm and the retainer prevents too much extension of the spring. As the duct temperature increases, the pressure in the probe will increase in proportion to the increased temperature because of the expanded liquid. The diaphragm feels the pressure increase and at 190F (88C) the pressure is larger than the spring force and the switch will operate. When the temperature decreases to 160F (71C), the spring goes back suddenly. The switch will operate when the duct temperature increases. The switch will operate the circuitry to close the applicable modulating valve. This will also cause a yellow INOP light on the pilot's overhead panel, P5, to come on.


AeroEd LLC Aviation Education Resource Check Valves for the Trim Air Supply The check valve for the trim air supply includes two semicircular flappers connected to a pin that goes through the center of the valve housing. The flappers are vertical to the valve housing axis. The flappers, pin, and flapper stop pin are installed in the one-piece valve housing. A flow arrow, on the side of the valve housing, shows the direction of the correct airflow. The flow of air in the direction of the flow arrow will open the flappers until they touch the stop pin. The opposite flow of air will close the flappers. When the valve is closed, it prevents the flow of air in the opposite direction.

Zone Temperature Selectors Each zone temperature selector has a selector shaft at one end of the housing. A knob and a twelve-pin connector are installed on opposite ends of the selector shaft. A name plate and a wire diagram label are attached to the housing. The selector includes a potentiometer, switches, and a cam assembly. Turn the temperature selector switch to get the AUTO or OFF temperature control mode. In the AUTO mode, turn the knob between C and W to select the temperature between 65F (18C) and 85F (29C).



Pressure Regulating Valve for the Trim Air System The pressure regulating valve for the trim air system is a three-inch diameter butterfly valve. The valve is electrically controlled and pneumatically operated. The pressure regulating valve controls the pressure of the trim air to 4 PSI above the cabin pressure. The TRIM AIR switch-light on the P5 panel, controls the pressure regulating valve. The regulating valve operates with 28-volts DC power. Push the switch-light to the on position to open the valve. Push the switch-light to the off position to keep 28-volts DC power away from the valve. With the switch-light in the off position the valve closes and the yellow OFF part of the switch-light comes on. The level C message, TRIM AIR, is also shown on the EICAS display. The valve can be manually opened if the cam is turned counterclockwise (CCW). The cam can be locked with a lock wire, to keep the valve in this position. The valve can be manually closed if the cam is turned clockwise (CW). The cam must be locked with a lock wire to keep the valve in this position.



The Modulating Valve for the Trim Air The modulating valve is a 1.75 inch diameter, electrically operated valve. Three modulating valves for the trim air system are installed in the mix bay at the aft end of the forward cargo compartment. The valves control the flow of hot air to their related zones: flight deck, forward cabin, and aft cabin. The removal and installation for each valve is the same. The valve may be manually opened or closed, the manual knob is turned CW to open and CCW to close.



Zone Temperature Controller The zone temperature controller is a microcomputer that contains all of the built-in-test-equipment (BITE) switches, fault indication lights, and BITE instructions. Two handles at the front of the controller help in the removal/installation. Three posts in the 125-pin connector, at the rear of the controller, are in a different position. This will prevent the installation of the controller at the incorrect location. Nine circuit cards on a primary circuit board contain the circuits for the controller. The zone temperature controller controls the temperature with the AUTO adjustment of the temperature selector switches. The controller also automatically and continuously monitors faults and supplies manual operation of the BITE. These controls supply the indication of internal controller failures and can isolate and monitor the failure of line replaceable units (LRUs). Red lights show defective LRUs during a BITE check. An internal memory supplies on-line BITE data. The BITE will monitor and keep LRU faults for 10 flights.



CONDITIONED AIR DISTRIBUTION SYSTEM

The main distribution manifold consists of a mix manifold, ducting, and a ground-air-service connector. The mix manifold is supplied with cold air from the air conditioning packs and warm air from the recirculation system. Then it mixes the air and distributes it to the passenger compartment, lavatories, and the galleys. The mix manifold also provides humidity control by extracting water from the combined airflow. Air from the left-air-conditioning pack can bypass the mix manifold. This conditioned air flows into the flight-deck-distribution duct and is distributed directly to the flight compartment. Whenever the airplane is parked, the air conditioning packs do not have to be used. Conditioned air can be supplied to the mix manifold through the ground air service connector. The conditioned air can be supplied by any standard air-conditioning ground cart.



Mix Manifold The mix manifold sits immediately aft of the forward cargo compartment aft bulkhead. Cylindrical in shape with a domed top, the manifold stands about 44 inches high and 24 inches in diameter. The manifold is constructed of thermosetting resin-impregnated Aramid fiber fabric. Three inlet ducts enter the mix manifold's lower section. The inlet ducts allow only tangential airflow into the manifold. Four 8.5 inch diameter outlet ducts exit the manifold from the upper section and channel the airflow to the conditioned air distribution ducts. A spacer between the bottom of the mix manifold and the airplane skin has a hole to drain condensed water from the manifold.

Ground Conditioned Air Connector The ground-conditioned-air connector allows conditioned air to be supplied directly into the mix manifold from a ground air cart. The connector consists of an eight-inch-diameter receptacle, a cover, and a swing check valve. The connector is on the underside of the fuselage, just forward of the left-air-conditioning pack. Conditioned air from the ground cart forces the swing check valve to open. The check valve automatically closes, but does not seat, whenever pressurized ground air is not available. The check valve is spring loaded so it only seats when the air conditioning packs operate (i.e. a pressurized system).



Flight Deck Conditioned Air Distribution The flight-deck-conditioned-air-distribution system supplies conditioned air to the flight deck to provide a comfort-controlled environment for the flight crew. The system consists of a flight-deck-conditioned- air-distribution duct, floor registers, individual crew gaspers, windshield diffusers, and an overhead register. The conditioned air is supplied to the flight deck area by the flight-deck-distribution duct. Then it is distributed throughout the flight deck by the registers, gaspers, and the windshield diffuser. Conditioned air from the left-pack-outlet duct flows into the flight-deck-distribution duct before it enters the mix manifold. In the flight-deck-distribution duct, the conditioned air mixes with trim air and flows to the flight deck. When the left-air-conditioning pack is not operating, the conditioned air can still enter the flight-deck-distribution duct. If only the right-air-conditioning pack is used, conditioned air flows into the mix manifold, and then exits the manifold through the left-pack-outlet duct and flows into the flight-deck-distribution duct. If only a ground cart is used, conditioned air flows into the mix manifold, and then exits the manifold through the left-pack- outlet duct and flows into the flight-deck-distribution duct (same as the right-air-conditioning pack).

Floor Registers The flight deck floor perimeter contains four floor registers. All outlets attach to flexible ducting. Air flows through the flexible ducting into the outlets. The outlets then disperse the air throughout the flight deck.

Overhead Register The overhead register mounts in the ceiling of the flight deck, in between halves of the overhead circuit breaker panel P11. The register assembly directs airflow in three different directions within the flight deck. Silicon sponge seals, between the plenum and the register, ensure an air-tight assembly. Conditioned air enters the overhead outlet from two inlet ducts on the top side of the plenum. Air then flows through the baffle and the nozzle disperses the air to the flight deck.

Windshield Diffuser The overhead drip shield contains the forward windshield diffusers. The diffusers incorporate an airflow straightener, a baffle plate, and a nozzle to ensure uniform distribution of air over the windshield. The sidewall panels contain the side window diffusers. The diffusers consist of a Nomex honeycomb air grille.



Gaspers The flight deck has four adjustable gaspers. There are 2 gaspers in the forward end of the cockpit, on the outboard side of the captain's station and first officer's station, respectively. A third gasper is located below and aft of the number 3 window, on the left side of the cockpit. The fourth gasper is mounted in the ceiling, to the right of the overhead circuit breaker panel P11. All gaspers consist of a drilled ball within a socket and an adjustable valve to control airflow volume.

Air Inlets Four air inlets, two on each side of the flight deck (L, R) provide supplemental heated air to the flight deck. The inlets are made of epoxy resin-impregnated aramid fabric.



Passenger Cabin Conditioned Air Distribution The passenger cabin conditioned air distribution system channels air from the mix manifold throughout the passenger cabin. The distribution system provides a comfortable environment for the passengers. The distribution system consists of sidewall risers, overhead ducts, overhead outlets, sidewall outlets, and return air grills. Conditioned air from the mix manifold mixes with trim air and enters four sidewall risers (two on each side). The air then flows through each sidewall riser into the overhead duct. Air is dispersed into the passenger compartments from the overhead duct through overhead outlets located along the overhead duct, and sidewall outlets located under the stowage bins. Gasper outlets, connected to the overhead ducts, disperse conditioned air into each lavatory. Adjustable outlets disperse conditioned air into the galley areas. Air exits the passenger cabin through the return air grills located in the sidewalls near the floor.

Sidewall Riser Ducts The sidewall risers are rectangular, 1.5 by 17.5 inch ducts located in the wall lining of the passenger compartment, just aft of the wing leading edge. Three-ply Kevlar and a thick honeycomb wall make up the riser ducts.

Overhead Duct The overhead ducting extends the full length of the passenger cabin. The ducts are made of rigid plastic foam. Adaptor assemblies attach the main overhead duct to each overhead outlet.

Sidewall Outlet Ducts The sidewall outlets are attached to the main overhead duct by smaller, 1.5 inch diameter flex ducts. The ducts are made of silicone rubber-impregnated fiberglass.

Return Air Grills The return air grills include a grill assembly and a screen. The air vents in the return air grill allow air to escape from the passenger compartment into the lower lobe of the airplane. This allows air to re-circulate and to leave the passenger compartment if there is a rapid decompression.

Overhead Outlets The overhead outlets consist of a flow divider and a blade inside a housing. The flow divider and blade break up the airflow to prevent drafts in the passenger compartment.

Sidewall Outlets The sidewall outlets consist of an air deflector inside a housing. The housing and air deflector disperse the air flow as it enters the passenger compartment.

Galley and Lavatory Outlets Separate adjustable outlets provide conditioned air to galley areas and non-adjustable gasper outlets provide conditioned air to each lavatory.



CABIN AIR RECIRCULATION SYSTEM

The recirculation system consists of two separate systems. The left recirculation system provides draw-thru cooling for the forward exhaust Electrical/Electronic (E/E) equipment cooling system. The right recirculation system provides recirculation of conditioned air for the passenger cabin. Re-circulated air from both systems mixes with conditioned air from the cooling packs in the mix manifold. The 50/50 mixture of fresh conditioned air and re-circulated air is distributed through the passenger cabin. The use of re-circulated air improves airflow without placing an undue load on the air supply source or the cooling packs. Both recirculation systems contain a filter assembly, a recirculation check valve, a recirculation fan, a current sensor, and ducting. The right recirculation system draws air from the passenger cabin through the return air grilles, into the forward cargo compartment sidewalls. From there it is drawn

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